Construction of heating surface of waste heat boiler for metal refining furnace

ABSTRACT

A waste heat collecting water wall in which boiler tubes are placed close together to absorb the waste heat from a metal refining furnace in which filler rods fill the space between the adjacent tubes and provide a substantially flat wall on which dust collects and can easily be removed because there are no deep indentations in the wall surface in which the dust from the furnace can collect and the wall is sufficiently flexible so that collected dust can be removed by vibration and/or by rapidly moving air.

United States Patent [191 Ojima et al.

[ CONSTRUCTION OF HEATING SURFACE OF WASTE HEAT BOILER FOR METALREFINING FURNACE [75] Inventors: MasakiOjima, Akashi City;

Ryouichi Otoyo; Tomohiko Shiraishi,

both of Kobe City, all of Japan 73] Ass i gnee: Kawasaki JukogyoKabushiki Kaisha, Kobe, Japan [22 Filed: Aug. 9, 1971 T 21 Appl. No.:169,910

[52] U.S. C1. 266/43, 266/35 [51] Int. Cl. C21c 5/46 [58] Field ofSearch 266/35, 31, 15, 16, 266/43; 122/6 A [56] References Cited UNITEDSTATES PATENTS 2,660,155 11/1953 Chapman 122/6 A 1,770,928 7/1930.Iacobus 122/6 A 1,791,064 2/1931 Murray 122/6 A 2,552,830 5/1951 Witzke122/6 A Oct. 16, 1973 3,303,876 2/1967 Berman et a1. 122/6 A 3,545,40912/1970 Young 3,320,931 5/1967 Durham 3,323,495 6/1967 Blaskowski3,380,728 4/1968 Baillie 266/35 FOREIGN PATENTS OR APPLICATIONS1,041,452 9/1966 Great Britain 122/6 A 1,110,439 4/1968 Great Britain122/6 A Primary Examiner-Gerald A. Dost Attorney-Milford A. Juten [5 7]ABSTRACT A waste heat collecting water wall in which boiler tubes areplaced close together to absorb the waste heat from a metal refiningfurnace in which filler rods fill the space between the adjacent tubesand provide a substantially flat wall on which dust collects and caneasily be removed because there are no deep indentations in the wallsurface in which the dust from the furnace can collect and the wall issufficiently flexible so that collected dust can be removed by vibrationand/or by rapidly moving air.

1 Claim, 9 Drawing Figures Patented Oct. 16, 1973 3,765,664

FIE-2 H97 1i h 11 f1 {i ii 1 1-1) 7 "A GE @6965 NVENTOR.

CONSTRUCTION OF HEATING SURFACE OF WASTE HEAT BOILER FOR METAL REFININGFURNACE This invention is regarding to the construction of the heatingsurface of the waste heat boiler, to be installed following the refiningfurnace for iron or non-ferrous metal.

High temperature gas, coming out from the refining furnace such assmelter, converter and etc., generally contains considerable amount ofdusts, but usually the furnace is provided with the waste heat boilerfor the purpose both for gas cooling and heat recovery.

Such waste heat boiler is always designed to be consisted of theradiation heating surface (water wall) and the convection heatingsurface, so that at first molten dusts carried over from the furnace canbe cooled down to be solidized, then brought into convection heatingsurface to prevent fouling of its surface.

But because often times removal of stuck dusts on the water wall is notsatisfactory, the gas temperature of the convection heating surfaceinlet goes up over the solidizing temperature of dusts, that causessticking and accumulation of dusts in considerable amount on theconvection heating surface, and the drop of heat transfer coefficientmakes a rise of boiler outlet gas temperature and draft loss through theboiler, eventually it necessiate to stop the boiler operation forcleaning, which makes the main cause of lowering of the overall plantoperation rate.

For this, the mechanical cleanings by means of the soot blowers, thehammering equipments (method to remove stuck dusts by knocking fromoutside of the boiler) or the hand lancing, are often performed duringthe operation both in the radiation and convection heating surfaces.

However, on the conventional membrane type water wall after mentioned,such methods of cleaning are rather difficult to be performedsatisfactorily. This invention is intended to faciliate the cleaning ofstuck dusts on the water wall and maintaining the clean condition of thewater wall, beside with many fabrication advantages.

This invention, on the basis of above-mentioned point, is to make almostflat surface at inner side of the water wall using special filler rodswelded continuously to boiler tubes, or using tangentially arranged fintubes, of which fin position is deviated to inner side of the waterwall, welded continuously at the each fin end.

By means of the feature of these water wall structure, the defects ofaftermentioned conventional water wall can be removed.

To make further explanations and to make clear of these points, thefollowing drawings shall be referred:

FIG. 1 shows a part of section of the water wall, actually adopted underthis invention.

FIG. 2 shows a part of section of the water wall, slightly modified ofFIG. 1.

FIG. 3 shows a part of section of the water wall using fin tubes underthis invention.

FIG. 4, 5 and 6 show a part of sections of the conventional water walls.

FIG. 7, 8 and 9 show a part of sections of the water walls in order toexplain of this invention.

FIG. 4 shows the conventional tangential tube arranged water wall,insulated with skin refractory mate rial (a) and covered with skincasing (12), or continuously welded between each boiler tube.

If the molten carried over dusts touch on this water wall, the dustsbecome solid by rapid cooling, but the adhesive force of the dusts onthe water wall is comparatively weak.

In this stage, the removal of the stuck dusts is rather easy. However,it is practically impossible to operate the dust removal equipmentsalways all over the water wall.

In the case, some of the stuck dusts on the water wall stay for a while,the best conductivity of the dusts is normally very low, therefore thetemperature of the stuck dusts surface rises very high.

The molten dusts coming out from the furnace are apt to stick on thestuck dusts surface due to its high temperature and finally all thesurface of the water wall is covered with the stuck dust layer firmly.

Under such conditions, the mechanical cleaning as above mentionedbecomes very difficult.

Even if the cleaning is possible to be carried out, the stuck dusts ofthe grooved space, shown by dotted lines on the boiler tubes, are verydifficult to be removed and are apt to remain.

For example, in the case that the dusts blown off by the soot blower, itis not only almost impossible to remove the dusts of the grooved spaceby blowing in the direction of an arrow mark (R), crossing to the axisof the tube and almost parallel to the water wall surface, but also muchpower is necessary to crack or break off the stuck dusts by shearing.

So if the dusts remain at any small parts on the water wall as describedabove, the dust sticking starts from these parts and again the wholewater wall is covered with the stuck dusts in a short period.

FIG. 5 shows a well known membrane type water wall comprised withcontinuously welded of the flat bar between boiler tubes.

FIG. 6 shows another well known membrane type water wall comprised withfin tubes, of which fin position is at the center of the tubes andcontinuously welded at the each fin end.

These conventional water walls have unevenness at the inner side surfaceof the water wall in cross direction to the axis of the tubes, thereforethese both have defect that the stuck dusts of the grooved space shownby dotted lines on the tubes are difficult to be removed and are apt toremain.

In this invention, considering the defect of above mentionedconventional water walls, the water wall is constituted of insertingfiller rods (12) shaped with a surface (b1) and (b2) as shown in FIG. 1,between each space of two adjoining tubes and welded both ends of thesurface (b-l) and (b-2) to the adjoining surface of tubes, provided thatthe above mentioned surface (b-l) is a plane parallel and adjacent tothe common contact plane of adjoining tubes and the above mentionedsurface (b-2) is a narrow plane close to the straight line connectingthe assumed centre of each adjoining tubes.

According to the construction of this invention, there is no groovedparts between the tubes of the water wall, which are shown by dottedlines in FIG. 4, 5 and 6, making nearly flat heating surface, so thatthe stuck dusts are easy to remove off and expose the whole water wallsurface by mechanical cleaning, and there is no place liable to have theremnant dusts.

That is to say, in the case that the stuck dusts are blown off by a sootblower, its blowing direction is almost parallel to the water wall, thesame effects of the stuck dusts removal are expected in spite of theblowing direction is parallel to the axis of the boiler tube or crossingto the same axis, and also there is less need to break off the stuckdusts by shearing.

Also, if the water wall is knocked from outside of the water wall shownan arrow mark (S) in FIG. 1 by a hammering equipment, the water walldeflects and vibrates in the vertical direction g-h to the water wallsurface due to the elasticity of the water wall.

In the case that the stuck dusts are removed by means of acceleration ofthis vibration, it is evident that the removal of the stuck dusts ismuch easier if the water wall surface is almost flat.

Furthermore, if the deformation of the water wall is larger, some crackstake place in the stuck dusts and easier to remove the dusts.

As has been described, this structure of the water wall is easy to keepthe water wall surface in clean conditiondue to easiness of removal ofthe stuck dusts and is difficult for carry over molten dusts sticks andaccummulates.

The tube arrangement pitch (f), the distance (e) between common contactplane of the tubes and the filler rod surface (b-l) is decidedconsidering the heat load, the gas temperature, the dust quantity,thedust components and etc.. If the operating conditions is severe, thevalue (e) will be nearly zero.

Here, as modified cases, are shown in FIG. 2 and 3.

FIG. 2 shows the case of which surface (b-l) of the filler rod is notflat plane but hollow arc surface, and FIG. 3 shows the case of whichfins substitute the above mentioned filler rod.

Each fin end (fi) of the fin tube (a) is welded continuosuly.

Also, the construction of this invention has outstanding advantages intechnical problem regarding to the thermal distortion at the time ofwelding of the tubes.

In the case of FIG. 1, if a filler rod (b) is placed between two tubes,the tube pitch can be definitely set and ensured, furthermore, thewelding can be applied to the surface (b-2) close to the straight linebetween the centres of adjoining two tubes, then carry out the weldingof the both ends of a surface (b-l).

This results gives greater rigidity by the previous welding of (b-2) andmakes the welding distortion of (b-l) surface smaller at the time ofwelding, so subsequent correction is rather easy.

FIG. 7, 8 and 9 are similar to this construction examples but they havefollowing defects:

FIG. 7 shows the water wall with boiler tubes (a) and continuosulywelded small rods (T).

FIG. 8 shows the water wall with boiler tubes (a) and continuouslywelded flat fins (f-b) of which fln position is deviated to the waterwall inside from the tube centre.

In these structures, there is a probability to cause disorder in tubepitches, and also decision of the position of the rod and flat bar isdifficult even after the tubes are properly arranged.

In the case of a rod, there is a limit to make it flat at the water wallinner side surface, and in the case of flat bar, when the heat load ishigh, the temperature of the flat bar also goes up and there is a dangerof the dust sticking.

Furthermore, there is an enough worry to have the thermal distortion dueto the welding heat.

FIG. 9 shows the water wall with boiler tubes (a) and continuouslywelded symmetrical filler rods (3).

In the case FIG. 9, there is a defect that the thermal distortion getsgreater on account of the welding heat from the primary welding side.

Also in the case that heat applying side is limited to only one sidesuch as water wall, it has disadvantage in the waste of the welding andmaterials, and still further disadvantage is that the effect of thehammering is reduced due to the more rigidity of the water wall.

This invention not only facilitates the cleaning the stuck dusts on thewater wall, but also facilitates maintenance of the cleaned conditiontogether with other fabrication advantages.

We claim:

1. A water wall heating surface for a waste heat boiler for waste heatfrom a metal refining furnace comprising a plurality of closely spacedsubstantially parallel tubes, long filler strips having a generally flatsmooth surface extending between the tubes closely adjacent the heat anddust engaging surface of the tubes providing with the tubes a generallyflat water wall, the generally flat surfaces of the strips beingsubstantially spaced from the axis of the tubes and closely adjacent theheat and dust engaging surface of the tubes and being substantiallytangent with the curvature of the tubes to increase the area of contactwith the gases the strips being rods of generally triangular crosssection and have arcurate surfaces corresponding to the 'arcuate surfaceof the tubes and abutting the tubes to obtain maximum heat transferbetween the rods and tubes, and the rods being welded to the tubes ateach dihedral angle thereof.

1. A water wall heating surface for a waste heat boiler for waste heatfrom a metal refining furnace comprising a plurality of closely spacedsubstantially parallel tubes, long filler strips having a generally flatsmooth surface extending between the tubes closely adjacent the heat anddust engaging surface of the tubes providing with the tubes a generallyflat water wall, the generally flat surfaces of the strips beingsubstantially spaced from the axis of the tubes and closely adjacent theheat and dust engaging surface of the tubes and being substantiallytangent with the curvature of the tubes to increase the area of contactwith the gases the strips being rods of generally triangular crosssection and have arcurate surfaces corresponding to the arcuate surfaceof the tubes and abutting the tubes to obtain maximum heat transferbetween the rods and tubes, and the rods being welded to the tubes ateach dihedral angle thereof.